1. Field of the Invention
The present invention broadly relates to optical systems for extracting energy from the gain medium of a laser and, more particularly, is concerned with a Fourier transform resonator which incorporates a Jinc-trap spatial filter which forms broad, high quality, modes that efficiently fill the laser gain medium.
2. Description of the Prior Art
The multipass character of laser oscillators greatly enhances the distortion potential of intracavity perturbations and aberrations. In particular, the effect of laser medium index inhomogeneities resulting from flow or pump variations, density or concentration fluctuations or simply thermal effects can degrade the wavefront exiting from a laser more than a similar extracavity disturbance. Similarly, the effect of mirror misalignments is greatly accentuated compared to normal (extracavity) optical trains.
In principle, the resulting wavefront errors can be corrected either intracavity or extracavity. However, these internal errors lead to both amplitude distortions and vignetting of the output beams that are not easily compensated with extracavity systems. Thus, it is essential to concentrate on intracavity correction systems. Further, the resulting intracavity errors may sometimes have an extremely high spatial frequency content. Since nonlinear conjugation and/or other nonlinear compensation systems offer excellent capability for correcting high spatial frequency distortion, as contrasted with conventional adaptive optics with deformable mirrors, it is preferable to use such systems in intracavity compensation.
Consequently, a need exists for an optical system, preferably of the nonlinear type, which compensates for aberrations in the laser gain medium in a simple way and at low cost compared with deformable mirror systems.